We propose two main specific aims. For the Aim 1 (a) we will measure biomechanical exposures across different psychosocial work environments for 120 computer workers, (b) From these data we will determine differences in exposure across environments and in doing so develop an exposure determinants model for keyboard, mouse, and passive idle tasks, (c) Then we will estimate and evaluate the prediction of average and cumulative exposure based on the determinants model and data from computer usage monitors. For Aim 2 we will test for associations between estimated biomechanical exposures and MSD health outcomes in an existing prospective cohort of 1821 (at baseline) computer workers. Specific psychosocial factors in the modern work environments including the office have been associated with higher prevalence and incidence of musculoskeletal disorders (MSDs). While several pathways may exist through which psychosocial factors impact the body and influence the onset and development of MSDs, one hypothesis, which is supported by numerous laboratory studies, suggests that increased stress originating from the psychosocial work environment increases one's exposure to biomechanical loads. Therefore, we propose to directly measure biomechanical exposure intensities (i.e. keyboard and mouse forces, hand, forearm, upper arm and shoulder postural dynamics and EMG of the trapezius and the wrist extensors) in 120 computer workers in the field spanning four different psychosocial environments. We will test for differences in biomechanical exposure intensities across these different psychosocial environments. In doing so we will develop a task-based (i.e. keyboard, mouse, and idle input device tasks) exposure determinants model. We will implement this model to estimate the average and cumulative biomechanical exposures for each participant of an existing two-year prospective cohort of 1821 at baseline (1582 at 1 year) office workers. The prediction will use task durations measured for each participant from computer usage monitor software programs. Public Health Relevance - This project will determine relationships between work environmental stressors including psychosocial and biomechanical factors, their interactions and the onset and development of musculoskeletal disorders for the modem office. The results will influence work place design and policies through the development of new evidence-based interventions.